Modes of granular segregation in a noncircular rotating cylinder - art. no. 011302

Axial segregation is a well-known example of segregation of granular materi als. However. at present, there is no conclusive explanation as to why it o ccurs. Most studies of axial segregation to date are based on cylinders wit h circular cross sections. and models focus on the character of the surface flow without accounting explicitly for the influence of any subsurface det ail. The present experiments demonstrate that the cross section of the mixe r has a significant influence on axial segregation and that subsurface dyna mics are, in fact, important. Unlike circular mixers, in square mixers the subsurface segregation patterns change with filling level. as does the time dependence of axial segregation. Furthermore, when radial segregation patt erns in noncircular mixers most closely resemble that observed for circular cylinders, the time dependence for axial band formation deviates: the most . These results challenge segregation theories of axial segregation that ig nore subsurface effects.